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When you do the math, that works out to $323,204 for a five-processor Linux machine with no memory, no disk, and no systems software, including z/VM or Linux. Because there is a big disparity between the cost of Linux on the mainframe and Linux on x64 boxes - excuse me, I forgot to speak perfectly GNUbie there: the disparity is between Linux support costs, since Linux is not an operating system and even if it were, it is free - let's add Linux to this barebones mainframe.

Given the discounts that Novell has cooked up and its 80 per cent market share on the mainframe, let's slap some SUSE Linux Enterprise Server 11 on the System z BC box. It costs $10,200 per engine, with discounts for a one-year standard support contract for SLES 11 on mainframes, so that adds another $51,000. (At list price, this would cost $75,000.)

If customers want to pre-pay for five years of support, they can get a support contract for $37,499, or $7,499 per engine per year. That's a big price drop, so let's be generous and do the comparison over five years. The bare System z machine with Linux and five years of support costs $510,699.

Let's now look at how many Xeon 5500 boxes with Linux and support that gets you, not including memory, disk, or hypervisor costs, as fairly as we can, given the lack of information about mainframe pricing. We'll take IBM's own System x servers, and use the System x3550 M2 rack server, the cheapest of IBM's Nehalem EP boxes. With two of Intel's four-core, top-end Xeon X5570 processors, the x3550 M2 costs $6,681. Main memory for this x64 box costs $109 per GB, and there is no way IBM is not charging a lot more for main memory on mainframes.

Now, toss on SLES 11, which is priced per machine, not per processor core, on x64 machinery. It costs $799 per box per year, or $3,995 per box for five years of support. So that comes to $10,676 for a bare-bones x64 Linux image.

What these system prices imply is that a fully-engined System z BC with five 3.2 GHz engines should be able to support the same number of Linux images as 48 of those System x3550 M2 rack servers, which have a total of 384 Nehalem cores running at 2.93 GHz.

I am not, of course, suggesting that the System z BC mainframe can support that number of images. As efficient and wonderful as z/VM may be, VMware's ESX Server 4.0 hypervisor is no slouch. It seems very reasonable that at the very least, an x64 box should be able to support one virtual machine per core with acceptable response times running Linux workloads. So that would work out to 384 Linux slices on those System x racks.

The question mainframe shops have to ask IBM is whether a five-processor System z BC can support something akin to this number of VMs running Linux concurrently - and then have Big Blue run benchmarks to prove it. I have my doubts, and until IBM provides some benchmark results that prove otherwise, so will Linux shops.

Traditional mainframe shops, and IT managers keen on maintaining their empires and taking away some power from the x64 server crowd, will no doubt talk about the operational benefits and savings that come from consolidating Linux workloads onto mainframes. These benefits are even harder to qualify and quantify, but that is how mainframe iron and other proprietary machines - and indeed Unix boxes - continue to sell against cheaper x64 iron. ®